Telegraph exchange system



April 16, 1935. F. s. KINKEAD 1,998,086

TELEGRAPH EXCHANGE SYSTEM Filed Dec. 29, 1953 2 sheets-Smet 2 IHIIPOLAR/ZE D POLAR/Z E D FOL AR/ZED N i' b.

( u' /Nl/ENTOR F$./(/N/(EAD ATTORNEY Patented Apr. 16, 1935 UNITE estaorsice signor to Beil Telephone Laboratories, incorporated, "Korir, N.Y., a corporatien of New York Application 29, i933, Serial No. 704,379

il iiairns.

llhis invention relates to teletypewriter switch-` ing circuits of themanually operated type ernplcying link circuits preferably in the formor" cord circuits for interchangeably connecting subscribers and tolllines and supervising connections set up over them.

Features of the invention are:

The use of a novel arrangement for transmitting supervisory signals overa toll line. There are three kinds of signals that need to betransmitted over a telegraph toll line for supervisory purposes: l. Acall signal; 2. A recall signal; and 3. A disconnect signal. t has beenproposed and claim is made elsewhere to the use or" selectors steppingsynchronously at each end of the line, these selectors being actuated byindependent sources of one-second impulses. In accordance with thisinvention the use or" independent synchronously operated timing systemsor devices is entirely eliminated.

A feature of the invention is that, instead of timing the open impulsesby a locally actuated timing device, the impulses which step theselectors are generated by self-interrupting relays at the centralorifice originating the supervisory signals and are transmitted over theline to the distant central cnice. The breaks or interruptions, of whichthese impulses consist, are long enough to cause the release of slowrelease relays designed to hold up over the break impulses sent bynormal operation or" printing telegraph inachines. The closed period ofthe line between breaks must be short to prevent breaking the series ofimpulses. The chance of such a series of breaks being produced by normaloperation of a printing telegraph machine is negligible.

The time required for the transmission of supervisory signals reduced. nthe past it has been the practice to use signals differentiated by thefact that the line was opened for various lengths of time. This time hadof necessity to be longer than any open period of the line nor- Inallymet during telegraph transmission. l'n accordance with this invention apeculiar combination of signals is used which will not be duplicated intelegraph transmission and which are of much shorter duration than thatpreviously used.

The time required to send the calling signal is unlimited in length. Inthe past the time required to operate the calling signal was limited bythe independently operated selectors. ln this invention a single openand closure of the line is used for this function and the time oftheropen is of no importance.

An open at the distant end or any part of the line will not mutilate orhinder the transmission of a recall or disconnect signal but will onlydelay its transmission.

rihis system is designed primarily for use on the toll lines ,ofteletypewriter exchange systems, where the main switching points areseparated by long distances and are connected by means of telegraphchannels including links or the Voice or high frequency carrier currenttype or of the open wire or metallic cable direct current type includingrepeaters. Y

General description In general, a teletypewriter exchange system is madeup oi a number of switching points which are connected one to another bymeans of toll lines. Each' switching point also has connected to it anumber of subscribers. Connections are manually made betweensubscribers, either direct as in the case of two subscribers connectedto the same switching point or exchange, or by means of toll lines whenthe subscribers are located at distant points.

It is necessary in order to supervise these interconnecting toll linesthatprovision be made for certain signals to be transmitted overk thesewhich are different in character than those transmitted over the lineduring transmission by the teletypewriters.

These signals, as covered in this description are: l. The call signal toestablish connection between one operator and another; 2. The recallsignal to reestablish communication between the operators after a callhas been completed and the operators have retired from the circuit; and3. The disconnect signal to indicate that the communication is completeand the cords can be removed. It is obvious that other signals can betransmitted for other purposes in the same Way and this `application isnot limited to these three.

Drawings In the accompanying drawings:

Fig. l shows a teletypewriter tool line termination at a central oice Aconnected to a telegraph repeater of a type which is well known in theart, and is therefore not shown in detail. This repeater is connectedover a telegraph channel to a similar repeater in central oihce B whichis in turn connected to a toll line termination which is identical withFig. l and is indicated by a block at central ofce B.

Fig. 2 shows a cord and operators circuit for use in connection withFig. l, from which the supervisory signals are sent and in which theyare received at the distant ofiice.

Fig. 3 shows a subscriber circuit connected to a subscribers lineterminating circuit at the central office. This circuit is shown only tocomplete the system and is not involved in the following description.

The teletypewriter machine used by the subscriber and the operator areof a known type in commercial use.

Originating a toll Zine callisignal.

Referring to Fig. 1, when the circuit is in the normal idle condition asshown, the transmission circuit is closed from battery in the telegraphrepeater over` the T lead, one winding of relay I, a pair of contacts onrelay 2,1a pair of contacts on relay 3, over the S lead to the oppositepolarity o1" battery in the repeater. Relay I is therefore held operatedto its contact 4 which'n turn holds relay i5 operated over an obviouscircuit. A similar condition is existent at central oice B.

If operator A wishes to call operator B the plug 5 of Fig. 2 is insertedinto jack 6 of Fig. 1. A circuit may then be traced from battery "I,winding of relay 8, the sleeve of plug 5, the sleeve of jack one windingof relay 3 to ground. Relays 3 and Il will therefore be operated. Thetransmission lead may now be traced from battery in the telegraphrepeater over lead T, one winding of relay I, a pair of contacts ofrelay 2,.a pair of contacts of relay 3, the ring of jack 6, the ring ofplug 5, a pair of contacts of `relay 8, a pair of contacts of relay 9,resistance IIJ, one winding of relay I I to the opposite polarity ofbattery on the contacts of relay I2.' The transmission circuit is nowestablished from the cord of central oiice A over the telegraph channelto a Fig. 1, in central oflice B which is in the idle condition.

The operator at A now operates key I3,.whichv in turn operates relay 9over an obvious circuit. The operation of relay 9 opens the transmissioncircuit at a pair of contacts,and.this open is transmitted over the lineto central oflice B. The line is `held open as long as key I3 isoperated but is closed as soon as key I3 is released which.

releases relay 9.

Reception of call signal At central oice B when the openline or callsignal is received, the operation of the telegraph repeater will removecurrent fromthe. normally closed T lead, and in consequence willdeenergize the winding of relay I. Relay I will moveto its contact itunder this condition by meansof the bias current in its other winding.Ihe operation of relay i to its contact I4 will operate relay I6 whichin turn will operate relay] 1, both over obvious circuits. Relay I5,however, will release and close a circuit to operate the rotary magnet.I8

which will step the Wipers I and 2 of the selector SEL to point I. Whenthe line closes, relay I will return to its contact 4, relay I6 willrelease and apply ground through the contacts of relay il, wiper I andcontact i of the selector, a pair of contacts and the winding of relayI9,"contacts of relay to battery on the contacts of relay 3,V causingrelay i9 to operate and lock up. Relay II also releases but being of theslow release type provides time for the operation of relay 'I 9. Relay I3 closes a pair of contacts which lights the lamp 2e indicating tooperator B vthat she is being called. Relay I9 also applies the busytest condition as described in Locke-Kinkead application Serial No.459,684 filed June 7, 1930.

The return of relay I to its contact 4 reoperates relay I5 removingcurrent from the rotary magnet I8. Likewise when relay I'I releases, acircuit will be provided for the release magnet 2i, from ground on thecontacts of relay it", contacts of relay I1, the winding of releasemagnet 2 I, a pair of the 01T normal contacts 22 which were operatedwhen the selector stepped, to battery at the contacts of relay 2. Theenergization of the release magnet will restore the selector to normaland open the 01T normal contacts.

Answering a, call signal The B operator will answer by plugging a plug 5of a cord circuit similar to that of Fig. 2 into jack 6 which willoperate relays 3 and 8 as previously described. The operation of relay 3will release relay I9 which in turn will extinguish the lamp 2E); It isto be noted that relay I will follow all teletypewriter signal impulsesbut relay i5 is of the slow release type and will not release on thesesignal impulses.

Transmission of a recall signal Assuming now that exchanges A and B areconnected together as has been described with one each of Figs. l, 2 and3 at each end and the operators have retired-from the circuit. Assumingalso that for some cause subscriber A has recalled operator A by a meansknown and described elsewhere and that it is necessary forA operator Ato recall operator B, operator A will originate this call byoperatingkey 23 which will apply ground through the contacts ofkey 24, contactsof relay 8, tip of plug 5, tip of jack G, contacts of relay 25, windingof relay 2, to battery on the lower contacts of relay 3, relay 3 beingoperated. Relay 2 will operate, and lock .up through the o normalcontact 22. Relay 2, when operated, will apply battery to thetip ortransmission lead looking toward the cord, and will complete the circuitfor the T lead, through its own contacts and the contacts of relay 26.Relay 2 will also apply battery to the winding of relayV 26 which willopen the T lead, causing relay I to go to its contact i4. Relay I5 willrelease causing relay 26 to release.

The release of relays I and I5 will, of course,

cause the wipers of the selectorto step to point I, in a mannerpreviously described. Relay l can v not operate, however, because itswinding is open at relays 2 vand 3. Relay 2 also can not unlock becausebattery is held on its locking winding by wiper 2. The release of relay26 will reclose the T lead, again operating relays I and i5, but theselector can not restore because the circuit of the release magnet 2I isopen atthe contacts of relay 2. The reoperation of relay I5 will againenergize relay 2E which will reopen the T lead again'releasing relays Iand I5 which will step the selector to point 2. W hen wiper 2 reachesthe second point, the locking .circuit for relay 2 is open and relay 2will release restoring the T lead circuit to the cord and closing it.This action reoperates relays I and I5 which restores the selector andcauses relay 25 to operate through point 2 of bank I of the selector.The operation of relay 25 Vcauses no action to take place in the cord atstation A, it being assumed that operator As typing key is thrown aswill be brought out in the discussion under the next heading.

Thus two breaks of-a Vdefinite duration are transmitted to the distantend.

Reception of a recall signal The reception oi the two breaks at centraloce B transmitted from operator A will release and operate relays l andl5 twice, stepping the selector wipers up to points 2. Wiper 2 will haveno function as relay 2 is not operated. Wiper l will, however, connectthe ground from the combination of released relay iii and released relayIl to operate relay 2c. Relay 25 will apply ground to a circuit throughthe tip of jack 6, tip of plug il, contacts of relay 8 which isoperated, contacts of key 24, contacts of key 23, which is not 0perated,contacts of relay 21 to battery through the winding of relay 28. Relay2B will operate, in turn operating relay 21. Relay 2l will lock up frombattery 29` through resistance 3l?, another winding of relay 22',contacts of relay 9`to ground at the contacts of relay 8. When theselector returns to normal at the expiration of the two pulses relay isreleased and relay 28 consequently releases. Under this condition, acircuit is formed from interrupter 3|, contacts or relay 2l, contactsor" relay 2S and lamp 32, which causes lamp S2 to flash from theinterrupter lil. Lamp 32 was, of course, maintained lighted while relayT58 was operated but only for a short time. The operator will answerthis signal by operating her typing key 33, which applies ground fromcontacts of key 34 to short-circuit relay 2l thus releasing it andextinguishing lamp 32.

Transmission of a disconnect signal Assuming the same initial conditionthat we had prior the transmission of a recall signal, if subscriber Adisconects it will be necessary for operator A to notify operator B toremove her toll line plug. To do this, operator A operates key 23 whichoperates relay 2 which in turn locks up through the oli` normal contacts22. In addition, however, she removes her plug which releases relay 3.The operation of relay 2 now actuates relay 2t causing the selector tostep in the manner previously described. When the wipers arrive on pointl, relay i9 can not operate because its operating circuit is open atrelay 2, and relay 2 will remain locked because of the battery on pointl of bank 2. When the wipers get to point 2 relay 25 will operate butproduce no result because the plug is out of the jack. Relay 2 willremain locked `from point 2 of bank 2 because battery is now present onthat point because relay 3 is released. When the wipers get to point 3,however, relay 2 will release and consequently the selector willrelease, it being noted that the circuit of point 3 of bank I is open atthe contacts of relay 3. Thus, three pulses are transmitted to thedistant end.

Reception of a disconnect signal At station B, the three pulses will bereceived in the same manner as the two pulses for the recall signal werereceived. However, when the wipers get to point 3, the circuit throughpoint 3 of bank l will be completed through the winding or relay 25, thecontacts of relay 3, the winding of relay Il to battery forming alocking circuit for relay il thus preventing its release andconsequently the release oi the selector. The Wipers are in consequenceheld on point 3, relay 25 is held operated and ground is held steadilyto complete the circuit through relays 2l and 28 of the cord. Lamp 32is, therefore, lighted steadily. This is the signal for the operator 'toremove the cord. The removal of the cord releases relay 3, whichreleases relay Il thus releasing the selector. The removal of the cordalso removes the ground from relays 2l and28. Relay 3 is also releaseddeenergizing relay 2l, thus the lamp 32 is extinguished.

It will be noted that in the transmission of either the recall ordisconnect signals if the line is opened elsewhere in the circuit, thisopen impulse will simply be added on toan open pulse originating in thetoll terminating circuit and the sequence of steps will continue as soonas this extraneous open of the line is closed.

The disconnect and recall signals referred to will appear at allstations on the line in the direction or" transmission. Thus, if tollline stations A, B, C and D are connected in a circuit in the ordernamed, a disconnect or recall signal transmitted from B toward C willappear at both stations C and D but not at station A, although theoperator at station B could transmit the signals toward and to station Aalso by manipulating. the splitting key in the cord circuit to applyground to the tip of the cord extending toward the station in question.

What is claimed is:

l. A teletypewriter system comprising a line circuit over whichtelegraph impulses are transmitted, line terminating equipment at theend of said line and devices for sending or receiving supervisorysignals thereover, comprising a stepping switch, relay meansunresponsive to normal telegraph signaling impulses associated with saidswitch, devices whereby said relay means cause said switch to step onceupon a single break impulse received over said line and twice upon twobreak impulses received over said line, etc., and means whereby when theline is not in use one predetermined number of break impulses producesthe call signal and means whereby when the line is in use otherpredetermined numbers of break impulses, respectively, cause recall ordisconnect signals.

2. A system comprising a line circuit over which telegraph impulses aretransmitted comprising a line, line terminating apparatus therefor, anddevices for sending and receiving supervisory signals comprising a cordcircuit and a stepping switch, relay means unresponsive to normaltelegraph signaling impulses associated with said switch, devicescontrolled by said relay means whereby said switch is caused to steponce upon a single break impulse received over said line with said cordcircuit unconnected to said line and twice upon two break impulsesreceived over said line with said cord circuit connected to said line incombination with devices controlled by said switch whereby one signal isactuated as a result of a single step of said switch and another signalis actuated as a result of two steps thereof.

3. In a printing telegraph toll line system, a toll line terminating ata central ofiioe, line terminating equipment connected to said line forsupervisory purposes, said equipment including a stepping switch andactuating relays, said actuating relays stepping said switch differentlyupon a given succession of line interruptions separated by a very shortclosure than if separated by a longer closure.

4. In a printing telegraph toll line system, a toll line terminating ata central office and ex tending to a distant office, toll lineterminating equipment including supervisory relays and also a multiplepoint stepping switch connected to said toll line at said oiiice,characterized in this that a line interruption of any lengthsubstantially greater than a normal telegraphing impulse causes saidstepping switch to step one step to give acall indication.

5. In a printing telegraph. exchange system, a line connecting twocentral oices, a cord circuit at each oice for connecting said linethrough to another line terminating atl each of said stationsfa key insaid cord circuit, and terminal equipment for said line at each endthereof, said terminal equipment including stepping switches, relaymeans in said terminal equipment controlled by operation of said keywhen the cord circuit -is connected thereto to cause said step pingswitch'to step twice and to send over the line two open conditions.'

6. A'systern according to claim wherein the two open conditionsreceivedat the distant end of said'line when the cord circuit thereat isconnected to said line cause the stepping switch `l`thereat to steptwice and whereupon upon reclosure of said line a circuit through arecall signal device is energized.

'7. In a printing telegraph system, a line connecting two centraloilices, a cord circmt at each oiiice for connecting said line throughto another line terminating at each oi said stations, a key'in-said cordcircuit and terminal equip ment for said line at each end thereof, saidterminal equipment including stepping. switches, re-

Mlay means in said terminal equipment controlled by the operation'ofsaidkey when the cord circuit is connected thereto followed by theimmediate disconnection of said cord circuit therefrom to cause saidstepping switches to step 'three times and to send over the line acorresponding number of open conditions.

3L A system according to claim 'Z wherein the three open conditionsreceived at the distant end of the line when the cord circuit thereat isconnected to said line cause the stepping switch thereat to step threetimes, energizing a disconnect signal circuit and remaining steppeduntil the disconnection of said cord from said line deenergizes saidsignal circuit and restores said stepping switch.

9. In a lprintingftelegraph toll line system, a toll line terminating ata central cnice, line terminating equipment connected to said line ateach end thereof for supervisory purposes, said toll line terminatingequipment being unresponsive to normal telegraph printer signals 1outresponsive to predetermined numbers of line interruptions to producerecall or disconnect signals, said circuit having stepping switchesresponsive to saidk line interruptions of any length to produce saidrecall or disconnect signals, characterized in this that the steppingswitches various stations are not synchronized whereby a great andabnormal timeI duration of an apen impulse upon said line may delay butdoes not prevent proper stepping of said stepping switches.

FULLERTON S. KINKEAD.

